This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This small source was found in an English documentation from 1970. The diodes can be 1N4002 for...
-- We find this configuration very simple in a previous American publication of 1973. The...
This double T oscillator configuration can employ operational diamonds and the symmetrical supply...